A population bottleneck is an event that drastically reduces the size of a population. The bottleneck may be caused by various events, such as an environmental disaster, the hunting of a species to the point of extinction, or habitat destruction that results in the deaths of organisms.

Evolutionary ideas came to prominence in the early 19th century with the theory (developed between 1800 and 1822) of the transmutation of species put forward by Jean-Baptiste Lamarck (1744-1829). At first the scientific community – and notably Georges Cuvier (1769 – 1832) – opposed the idea of evolution.

Charles Darwin’s theory of evolution states that evolution happens by natural selection. Individuals in a species show variation in physical characteristics. As a consequence those individuals most suited to their environment survive and, given enough time, the species will gradually evolve.

A bottleneck is a point of congestion in a production system (such as an assembly line or a computer network) that occurs when workloads arrive too quickly for the production process to handle. The inefficiencies brought about by the bottleneck often creates delays and higher production costs.

Because of the high frequency of new mutations in humans, there is no need to assume an increased mutation rate to explain the finding of multiple mutations responsible for the prevalence of a disease in an isolated population.

Genetic drift does not take into account an allele’s adaptive value to a population, and it may result in loss of a beneficial allele or fixation (rise to 100% frequency) of a harmful allele in a population.

The consequences of genetic drift are numerous. It leads to random changes in allele frequencies. Drift increases the amount of genetic differentiation among populations if no gene flow occurs among them. Genetic drift also has two significant longer-term evolutionary consequences.

Genetic drift describes random fluctuations in the numbers of gene variants in a population. Genetic drift takes place when the occurrence of variant forms of a gene, called alleles, increases and decreases by chance over time. These variations in the presence of alleles are measured as changes in allele frequencies.

Mating closely related animals on purpose, like brother and sister or father and daughter matings, results in an increased probability that the offspring of the mating will receive the same allele from both parents. This results in increased homozygosity, and thus in inbreeding.